High speed rotating devices are often driven by electric motors or internal combustion engines. The use of radial in-flow hydraulic turbines to drive fans and pumps is well known to the art. For example, U.S. Pat. No. 3,607,779 by Earle C. King illustrates the use of a radial inflow water turbine at the front end of the shaft driving a relatively low pressure rise axial fan and a foam concentrate pump at the rear end of the shaft. U.S. Pat. No. 4,597,524 issued to Stig L. Albertson describes a snow making machine with air flow fan being belt driven by a multistage water turbine. U.S. Pat. No. 3,141,909 by H. A. Mayo, Jr. describes turbine drive for cooling tower fan utilizing an radial outflow water turbine driving a fan.
There are a number of manufacturing companies which produce portable radial inflow hydraulic turbines. Hale Fire Pump Company of Conshohocken, Pa. and Coppus Portable Ventilation and Turbine Division of Tuthill Corp. of Millbury, Mass. produce radial inflow hydraulic turbines for driving air ventilation fans. Gilkes Inc. of Seabrook, Tex. produces radial inflow hydraulic turbines to drive liquid removal and transfer pumps.
A large majority of these turbines are driven by water pressure between 100 and 200 psi, which is a standard fire hose pressure in the U.S., on shore and aboard the ships. These are relatively low pressure turbines and are relatively large in size and weight.
Their method of construction cannot tolerate very high hydraulic pressures and high hydraulic fluid temperatures. They are also not suitable for speeds required to drive typical very high speed compressor superchargers.
A hydraulic Pelton turbine has been employed to drive a turbocharger in UK Pat. No. 2,127,897 by Ricardo Carricante. Main disadvantage of this concept is that the Pelton turbine cannot be submerged in hydraulic fluid, which would cause drastic loss in efficiency. This requires high positioning of the turbocharger above the engine oil sump in order to facilitate an air cavity around the turbine wheel and drainage of relatively large oil flow that drives the turbine. This situation sometimes causes air entrainment and foaming problems in the engine oil. Other motors considered as drives, such as vaned motors, are usually not long lived at typical high turbocharger speeds.
A radial inflow supersonic turbine with nozzle holes in an axial-tangential arrangement is shown in the U.S. Pat. No. 4,066,381 by E. R. Earnest. The nozzles here are drilled through a flat plate under a combined axial and tangential angles. Such manufacturing methods are usually very expensive because of tight tolerances needed to position the exit of the combined angle nozzles accurately and the fact that the supersonic section must be drilled separately from the other initially drilled hole from the first side. The radial-axial turbine wheel has three dimensional geometry which makes the wheel manufacturing very expensive.
Superchargers are air pumps or blowers in the intake system of an internal combustion engine for increasing the mass flow rate of air charge and consequent power output from a given engine size. Turbosuperchargers (normally called turbochargers) are engine exhaust gas turbine driven superchargers. When superchargers are driven mechanically from the shaft of the internal combustion engine, a speed increasing gear box or belt drive is needed. Such superchargers are limited to a relatively low rotating speed and are large in size. Paxon Blowers and Vortech Engineering Co. are marketing such superchargers. Fixed gear ratio superchargers suffer from two very undesirable features: 1) there is a sharp decrease in boost pressure at low engine RPM because boost pressure goes generally to the square of the speed of rotation, and 2) it is generally difficult to disconnect the supercharger from the engine when the supercharger is not needed.
There is a great need in the engine industry for an efficient method for driving compact, light weight superchargers. According to an article at page 27 of the August 1993 issue of Popular Science, Miller cycle engines, developed by Mazda require "a compact, high-efficiency air compressor--conventional turbochargers and superchargers just can't generate the volume of air required". The article further states, "Mazda teamed with heavy equipment manufacturer Ishikawajima-Harima Heavy Industries Co. to develop a belt driven, screw-type compressor supercharger. The new supercharger is expensive, which is one reason Mazda doesn't plan to use the Miller-cycle engine in small cars. Lean-burn technology makes more sense there . . . ".
Detroit Diesel Corporation is employing a low inertia ceramic turbocharger turbine wheel to provide a more responsive turbocharger. In their recent literature promoting their Series 50 turbo diesel engine they state, "The lower inertia ceramic turbine wheel is used to provide a more responsive turbocharger for faster response and higher performance so critical for transit bus operation."
Mercedes-Benz AG has recently announced that they were using a mechanically driven wankel rotary type air compressor made by Ogura as a supercharger. The wankel supercharger is positioned upstream and in series with a standard supercharger. The supercharger operates at a fixed speed at a 5.5:1 ratio with the engine speed.
There is a great need for supercharging of present turbocharged diesel engines. In the low RPM range, the currently available turbocharging systems are not very effective in producing sufficient engine manifold pressure and power required for satisfactory vehicle acceleration and exhaust smoke reduction. This applies especially to "stop and go" type services, such as city buses and trash collecting trucks. A thermodynamic cycle analysis of a typical truck turbodiesel engine shows that even with modest 2 to 3 psi supercharging applied in series to the inlet of the existing turbocharger compressor in the low engine RPM range, the existing turbocharger pressure ratio increases exponentially mainly due to a large increase in turbocharger turbine power.
A typical 250 HP four stroke turbodiesel engine with supercharger/turbocharger staged in series, is projected to experience a 61% increase in power at 800 RPM and 72% at 1000 RPM but drops off to 67% at 1200 RPM and about 33% at 1400 RPM. Many presently available direct driven superchargers cannot be disconnected when not needed, which would generally occur above 1400 RPM, when turbocharger system alone, starts being effective. Not being able to disconnect the supercharger produces drag on the engine as the engine speed increases up to full speed which is usually around 2500 RPM. When clutches are provided to provide disconnects, the frequency of the disconnects may result in short clutch life.
A popular exhaust driven turbocharger is Model TO4B 3S supplied by Turbonetics Inc. This unit can produce compressor ratio (output pressure/atmospheric pressure) of 2.50. The various parts of this unit can be purchased separately from Turbonetics as listed in its catalog.
Gear driven and belt driven oil pumps are commercially available in the 10 to 20 HP range for producing oil pressures in the range of 500 to 2,000 PSIG at flows of 20 to 40 GPM.
The Applicant has been issued a United States patent (U.S. Pat. No. 5,013,214) for a high speed water driven fan. Disclosed in the specification was a turbine which produced 4 horsepower at 10,000 RPM. The specification referred to and provided guidance for increased horsepower designs and higher RPM's. Relatively low stress levels and low operating temperature of the turbine wheel driving the fan has allowed for the 2.07 inch diameter wheel to be made entirely of Delrin type plastic.
It is known that plastic turbines are generally less expensive to produce than metal turbines, but at very high rotating speeds and high temperatures plastic turbines do not have sufficient strength to provide reliable performance. Very small steel turbine wheels are difficult to manufacture using standard milling procedures and electro discharge machining is very expensive. Typical production costs of making a 0.80 inch diameter turbine wheel with 34 blades is on the order of $300. Sintering is another possibility, but its tooling costs would be very high.
Utilization of high temperature thermoplastics to make very high speed turbine wheels would lower the cost significantly since the blades could be milled with conventional techniques, but the combined effects of high centrifugal stresses and high oil temperatures would cause the plastic to deform and creep with time, especially in the hub area where precision fit between the shaft and the wheel bore is required at all times.
What is needed, is a very high precision, rugged, low cost miniature turbine wheel and nozzle, that can withstand high hydraulic fluid pressures and temperatures while operating at speeds of 50,000 to 150,000 RPM while maintaining its basic dimensions and structural integrity for a long time with the capacity to respond very quickly on demand.